Add skeleton classes for hardware event flow (B1)

java/src/com/android/inputmethod/event/Event.java

java/src/com/android/inputmethod/event/EventDecoder.java

java/src/com/android/inputmethod/event/EventDecoderSpec.java

java/src/com/android/inputmethod/event/EventInterpreter.java

...c/com/android/inputmethod/event/HardwareEventDecoder.java

...droid/inputmethod/event/HardwareKeyboardEventDecoder.java

...c/com/android/inputmethod/event/SoftwareEventDecoder.java

java/src/com/android/inputmethod/latin/LatinIME.java